Brian Neel, Joern Schneeweisz, and Jeff King discovered that Git did
not properly handle host names in 'ssh://' URLs. A remote attacker
could use this to construct a git repository that when accessed could
run arbitrary code with the privileges of the user.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 17.04:
git 1:2.11.0-2ubuntu0.2

Ubuntu 16.04 LTS:
git 1:2.7.4-0ubuntu1.2

Ubuntu 14.04 LTS:
git 1:1.9.1-1ubuntu0.6

In general, a standard system update will make all the necessary changes.